The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
The selection of battery electrode active materials includes considerations such as the desired energy or power output for and any size limitations of the particular device incorporating the battery. With rechargeable batteries, capacity and rate capability, or the quantity as well as the rate at which the battery receives and delivers an electrical charge, are also considered. In electric vehicles or other high-power applications, both the capacity and rate capability are the major priorities because of the extended range and high charge as well as discharge rates demanded by these applications.
With respect to lithium batteries, there is a loss of capacity and rate capability because after the initial charge and discharge cycles of a new battery, there is an “initial cycle irreversibility” or a loss of 5 to 50% of available lithium. Thus, the initial cycle irreversibility decreases the storage and deliverable capacity of the battery for subsequent charges and discharges. This causes a marked decrease in the capacity of subsequent charge and discharge cycles. To compensate for the initial cycle irreversibility and decrease in storage capacity, the battery size may be increased. However, these and other compensations have shortcomings.
In lithium-ion batteries, energy is supplied by a diffusion of lithium ions through the electrolyte from anode to cathode in the battery. During charge and discharge operation, the lithium is intercalated into or from the active electrode material. Because automotive applications have varying energy storage and energy power requirements depending on the type of vehicle, the acceleration, power requirements, and the rate of diffusion or withdrawal of lithium varies during operation of the vehicle. The diffusion of lithium, and in particular the gradients in its concentration thereof, gives rise to diffusion induced stresses in the electrode material. These stresses reportedly damage the electrode material leading to entrapment of lithium responsible for providing the capacity; and reduction in electronic and ionic conductivities which are essential for transporting the active lithium within the electrode material.